Comment 4 for bug 1362452

just to here to confirm that the problem is still ongoing on 16.04 Ubuntu Studio
Steps to create the issue:
1) go to menu editor
2) change a menu item, for example: changing "lmms", to "lmms -s 48000"
3) save the menu
4) go to the menu, observe that Graphics and Video folders have vanished. Audio has only "lmms" entry

additional observations:

renaming ~/.config/menus/xfce-applications.menu to ~/.config/menus/xfce-applications.menu.bck results in other menus restored. However now there is 2 "Audio" folders. one with single application, the other with all expected applications.

removing
~/.config/menus/xfce-applications.menu.bck
~/.config/menus/applications-merged/user-ubuntustudio-audioproduction.menu
~/.config/menus/gnome-applications-merged/user-ubuntustudio-audioproduction.menu
reverts the menu back to correct structure.

.desktop file of lmms seems to be correctly created/modified throughout this process.